<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>

    <script>

        var n = 7 ;

        // 假设是一个质数
        var flag = true ;

        for(var i = 2 ; i < n ; i++) {
            if(n % i === 0) {
                flag = false ;
                // 已经不是质数了就提前结束
                break ;
            }
        }

        flag ? alert('是') : alert('不是') ;

    </script>
    
</body>
</html>